Safety devices exist which prevent the accumulation of gases inside the container of a sealed accumulator and allow their evacuation when the internal pressure exceeds a pre-determined value.
The known safety devices are generally constituted by valves. Document U.S. Pat. No. 5,523,178 describes an accumulator valve. However, this valve has the drawback of being of complex design. When of simple design, valves have the disadvantage of opening only for high pressures, or opening for only a narrow range of pressures.
In addition, it is necessary for an accumulator safety device to also act as a circuit-breaker suitable for stopping the overload reaction quickly by interrupting the electric circuit in the accumulator. The circuit-breaker function also allows the appliances connected to the accumulator to be insulated electrically and irreversibly.
Document U.S. Pat. No. 6,274,264 describes an accumulator safety device comprising on the one hand a circuit-breaker intended to interrupt the electric path between an internal electrode connected to the electrochemical bundle and a current output terminal when the pressure in the accumulator exceeds a pre-determined threshold; and on the other hand a valve constituted by a cover portion having thinner sections, suitable for tearing when the pressure in the accumulator exceeds another pre-determined threshold higher than the first.
In addition, a safety device for an accumulator is known from the document U.S. Pat. No. 6,392,172, comprising a circuit-breaker integrated into a side wall of the container and suitable for interrupting the electric path between an internal electrode connected to the electrochemical bundle and a current output terminal when the pressure in the accumulator exceeds a pre-determined threshold.
Document FR-A-2,756,421 describes a circuit-breaker terminal which passes through the cover of an accumulator container. The circuit-breaker comprises a circular rupture component having weakened points on its periphery and welded at its centre to a membrane. In normal operation, the membrane with the rupture component ensures the electric continuity between the internal electrode and the current output terminal. In the event of malfunction and an increase in the pressure inside the accumulator container, the membrane abruptly deforms, taking with it the centre of the rupture component which breaks on its periphery between its weakened points. Electrical continuity is thus interrupted, but tightness preserved by the membrane.
The known circuit-breaker devices limit the passage of the current delivered by the accumulator to around 20 A due to a high internal resistance of the order of 0.5 to 2 mΩ. The circuit-breakers of the prior art are dimensioned to break or deform at a limit pressure value of the order of 7 to 10 bar, in order to fulfil their circuit-breaker function and interrupt the electric path. They must not therefore be too thick. Against this, they cannot conduct a large current, for example of the order of 50 A, for applications with high-power elements.
There is therefore a need for a sealed accumulator equipped with a circuit-breaker safety device which is of simple design and can be applied to large currents for high-power appliances.